1. Field of the Invention
The present invention relates to a novel zoom lens and imaging device, and more specifically, to a technology for increasing the zoom ratio of a zoom lens using a so-called bending optical system to reduce the thickness in the direction of the optical axis of the incident light.
2. Description of the Related Art
In recent years, imaging devices such as digital still cameras, which use solid-state imaging elements, have become popular. As digital still cameras become popular, they are expected to have a higher image quality. Demands are growing for digital still cameras having a particularly large number of pixels to have lenses for taking pictures, in particular, zoom lenses, having a good imaging performance to be used with solid-state imaging elements having a large number of pixels. Further, digital still cameras are expected to be small. Accordingly, compact and high-performance zoom lenses are desired. Some cameras have been further reduced in thickness by using a prism disposed between lenses to bend the optical axis of the optical system.
In addition, demands for a higher zoom ratio are strong. However, an increase in zoom ratio leads to degradation in image quality due to hand shake, which results from unstable holding of a thin camera.
Japanese Unexamined Patent Application Publication No. 2006-71993 discloses a zoom lens including five lens groups, namely, positive, negative, positive, positive, and negative lens groups, arranged in sequence from the object side to the image side. In the zoom lens disclosed therein, a fifth lens group is divided into two subgroups, namely, a negative lens subgroup and a positive lens subgroup. The positive lens subgroup is moved in a direction substantially perpendicular to the optical axis to shift images.